In recent years, flat panel display devices, such as liquid crystal displays (LCDs) and organic light emitting diode (OLED) displays are becoming increasingly popular as mechanisms for displaying information to operators of vehicles, such as aircraft. One of the reasons for this is that such displays are capable of providing very bright and clear images that are easily seen by the user in a broad range of environmental conditions, such as operating temperatures and ambient lighting conditions.
Active matrix (AM) OLED displays offer significant advantages over current AM LCD displays with respect to image quality and viewing angle. Additionally, AM OLED displays offer a faster response time, and are lighter, thinner, less expensive (i.e., no need for a backlight or color filters), and consume less power. However, there are technical issues associated with AM OLEDs that need to be resolved before the full potential of the technology is realized.
Currently, low-temperature poly-silicon (LTPS) thin film transistor (TFT) technology is typically used with AM OLEDs. While LTPS TFTs are appropriate for use in small, high resolution displays for mobile applications, it is considerably more expensive to produce large area displays, particularly compared to amorphous silicon (a-Si) TFT technology, which is generally used in large area, flat panel AM LCDs.
However, a-Si TFTs operate only in the n-channel mode. The OLED is typically on the source side of the TFT and has a common cathode architecture. Thus, any variations in the OLED device (i.e., the pixel) result in variations in the gate potential of the drive TFT, which in turn results non-uniform pixel luminance. An n-channel transistor, with the OLED on the drain side of the pixel circuit with a common anode architecture is ideally suited for driving AM OLED pixels. However, in the past, it has not been possible to fabricate AM OLED displays with a common anode architecture because of the difficulty in depositing the indium tin oxide (ITO)) anode layer on top of the organic layers of the OLED device stack. For example, deposition of an ITO anode layer onto the organic layers damages the organic layers due to exposure to oxygen during sputter deposition process.
Additionally, because of the low mobility of a-Si TFTs, the drive circuitry occupies significant surface area on the pixel, thereby reducing the pixel aperture ratio, and thus the average pixel luminance. As a result, the pixels are often operated at undesirably high voltage and power levels in order to achieve the required average pixel luminance, which reduces the useful life of the pixels.
Accordingly, it is desirable to provide a method and system for addressing these issues associated with the use of a-Si TFTs in OLED displays. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.